In conventional constructions of rotors of this type, the core of the rotor carrying the windings is formed by a stack of ferromagnetic sheets between a pair of flanges, the stack being fixed to the shaft of the motor. The stack is formed on its periphery with grooves into which the windings are inserted, the grooves being formed by alignment of notches in the ferromagnetic sheets.
The variation in size of a stack of the sheets must be within limited tolerances, i.e. approximately equal to the thickness of a sheet, for effective mounting of the rotor in motor by means of lock washers, snap rings or the like having the same function. These tolerances must be maintained if shifting of the rotor body is to be precluded and hence shimming is often necessary to fit the stack.